1. Field of the Invention
The present invention relates to a light intensity simulation method, a light intensity simulation program product, a recording medium and a designing method of a photomask which is used in photolithography in manufacturing a semiconductor device and the like.
2. Description of the Related Art
In manufacturing the semiconductor device and the like, various patterns formed in the photomask are transferred to a photosensitive resist formed on a substrate by photolithography. After this transfer, the photosensitive resist is developed, and processing of a wiring layer or the like is carried out using the patterns of the photosensitive resist as masks. In such photolithography, a projection exposure device of refraction optical system or reflection/refraction optical system is used.
Moreover, a method of carrying out light intensity simulation of such lithography has been adopted in order to understand the optical property of the transfer in advance. FIG. 17 is a schematic view showing a part of one example of the patterns of the photomask, and FIG. 18 is a schematic view showing the conventional light intensity simulation method with respect to the photomask shown in FIG. 17.
According to the conventional light intensity simulation method, when an exposure wavelength is 0.193 μm and four opening patterns 1 to 4 exist in a part of the photomask, as shown in FIG. 17, a rectangular area whose side length is about 2 to 10 μm is made to be a unit of calculation, as shown in FIG. 18. FIG. 19 is a graph showing the light intensity along the I—I line in FIG. 17, which is obtained by the conventional simulation method.
In recent years, a phenomenon called local flare is becoming a problem as the exposure wavelength becomes shorter. This local flare is caused due to an aberration of an exposure machine. However, a light intensity simulation method taking the influence by the local flare into consideration has not been established conventionally. For this reason, there is a problem that the light intensity simulation with high accuracy cannot be carried out. Accordingly, it becomes difficult to design the photomask for transferring desired patterns onto a photosensitive material such as the photosensitive resist.
In forming the various patterns in a microchip, the projection exposure device of refraction optical system or reflection/refraction optical system is used as described above. However, light whose optical path is different from the designed one is generated due to reflection and scattering of the surface and the inside of a lens of illumination optical system, mask, projection lens and the like, nonuniformity of a refractive index of lens material, and the like. Namely, stray light is uniformly caused over a whole area of one shot of about 20 mm2. This is a phenomenon called flare.
Moreover, in recent years, there are increasing demands for fining and high integration of the semiconductor device, and accordingly, light for exposure which is adopted in the projection exposure device is becoming shorter. In concrete, the light for exposure whose wavelength is 193 nm is adopted. Due to a peculiarity of lens material corresponding to such a short wavelength, it is becoming a problem that fog of light differs according to an opening area near a pattern, and local flare is generated depending on an exposure pattern. Such flare is referred to as the local flare, which mainly causes unexpected changes in a shape and a line width of the pattern to be transferred.